MHC Flashcards
Primary and secondary response
When there is a first encounter between the antigen and the virgin lymphocyte pool- only lymphocytes that can specifically recognise the antigen is stimulated to divide. These will either divide into memory cells or effector cells.
Then if the individual encounters the same antigen again at a later date, those memory cells will come into play producing a much faster and effective immune response.
What effector cells do B lymphocytes have
Plasma cells
What effector cells do T lymphocytes have
Helper T cells
Cytotoxic T cells
How do B cells recognise antigens?
B cells recognise antigen by their surface antibodies-
How do T cells recognise antigens
T cells recognise antigens by T cell receptors which means T cells on recognise part of the antigen that is present on the surface. We need the pathogenic derived peptides to be delivered to and presented at the cell surface level and this is done by a specialised glycoprotein known as a MAJOR HISTOCOMPATABILITY COMPLEX.
T cells recognise a combination of the MHC molecule and peptide fragments of an antigen.
What are the two classes of MHC
Class 1- HLA1 HLA2 HLA3- these are present on all nucleated cells including leukocytes.
Class 2- HLA DP, HLA DQ, HLA DR- these are present only on leukocytes that present antigens to T cells e.g. monocytes- cells that are a good at phagocytosis.
What are the clinical implications of HLA/MHC
1) Tissue grafting- important that there is good matching of the MHC make-up of the donor and the recipient. Even with 2 mismatches of the HLA type- kidney transplant success rate can go to 65%
2) certain HLA types are predisposed to certain diseases
3) Forensic medicine can use HLA makeup
Structure of MHC molecules
Two upper domains form a groove using hydrogen bonds in which the antigen sits.
Two lower domains are nearest to the transmembrane
What is the difference in the structure of MHC class 1 and class 2.
MHC class 1- has 3 alpha chains with a non-covalent association of a beta micro globulin. This allows the peptide binding cleft to be more open
MHC class 2- has 2 beta chains and 2 alpha chains.
What is the function of MHC class 1 and class 2
T cells can only see antigens in association with MHC proteins.
MHC Class 1- presents peptides to cytotoxic T cells. This is present on all nucleated cells- if a pathogen takes over the host, it makes its own cellular mechanism and produces peptides. These peptides are presented to the MHC class 1 which is on the cell surface- with antigenic material- it will cause the stimulation of cytotoxic T cells that activate trigger mechanisms.
MHC class 2- presents peptides to helper T cells. This is present on phagocytosing cells like monocytes- the peptides are packed into vesicles and MHC/TCR complex will cause the stimulation of helper T cells which will produce antibodies towards that specific antigen.
